1. Field of the Invention
The present invention relates to an idle intake control device for controlling an amount of intake air at the time of idling of an internal combustion engine.
2. Description of the Related Art
It has been known to arrange an idle intake control device in an intake system of an internal combustion engine to adjust the flow rate of the intake air at the time of idling (refer to for example Japanese Unexamined Patent Publication (Kokai) No. 4-1467). Such a first related art is shown in FIG. 1 and FIG. 2. In FIG. 1, air is fed to an engine 1 from the outside through an intake pipe 21 and intake chamber 22. The intake chamber 22 has a number of intake tubes 22a, equal to the number of cylinders of the engine, communicates with the cylinders of an engine 1 like a multi-cylinder gasoline engine. The space in the intake pipe 21 and the intake chamber 22 forms an intake passageway 2. The air from the outside is adjusted in amount by an intake regulating valve (throttle valve) 3 disposed in this intake passageway 2 and sucked into the cylinders of the engine 1.
The intake passageway 2 is also provided with a bypass connecting the upstream side and downstream side of the intake regulating valve 3. This is used as an idle intake passageway 4 at the time of engine idling when the intake regulating valve 3 is fully closed. In the middle of this idle intake passageway 4, an idle intake regulating valve 5 is disposed. The idling speed is precisely adjusted by finely adjusting the amount of the flow rate of the intake air fed to the engine 1 through the idle intake passageway 4.
The idle intake passageway 4 is usually formed inside a thick part of the wall of the intake passageway 2 as shown in FIG. 2, and is frequently of a bent shape or with step differences. Accordingly, in general, a vortex is apt to be generated due to a change of the passageway area downstream of the idle intake regulating valve 5. Similarly, if there is a step difference where the passageway diameter expands in the direction of advance of intake air in the idle intake passageway 4 downstream of the idle intake regulating valve 5, a vortex is generated downstream of the step. In the configuration of FIG. 2, step portions 61 and 62 exist downstream of the idle intake regulating valve 5. The passageway diameter changes considerably before and after the same. As indicated by the arrows in FIG. 2, vortices 7-1 and 7-2 are apt to be generated immediately after the idle intake regulating valve 5 and immediately after the step portions 61 and 62, respectively.
On the other hand, in FIG. 1, the combustion products stagnate in the intake chamber 22 downstream of the intake regulating valve 3 due to the blowback from the engine 1. There is a problem that the combustion products invade the idle intake passageway 4 due to the pulsation in the intake chamber 22 and the vortexes 7 shown in FIG. 2. Namely, the combustion products enter near the outlet of the idle intake passageway 4 due to the pulsation in the intake chamber 22 when the intake regulating valve 3 is opened wide. Further, if the vortexes 7 shown in FIG. 2 are generated in the idle intake passageway 4 when the intake regulating valve 3 is substantially fully closed, they ride on them and flow back in the idle intake passageway 4. Then, the combustion products are apt to adhere to the idle intake regulating valve 5.
Next, a second related art of the idle intake control device is shown in FIG. 3. In this example, a door-shaped idle intake regulating valve 5 forming a clearance by rotating or moving forward or backward in the axial direction is provided in the idle intake passageway 4 formed in the bypass passageway of the throttle valve 3. Air passes through the clearance and controls the idling speed of the engine (refer to Japanese Unexamined Patent Publication (Kokai) No. 6-101604, Japanese Unexamined Utility Model Publication (Kokai) No. 2-7369, or Japanese Unexamined Patent Publication (Kokai) No. 2-233815).
When an engine provided with such an idle intake control device of the related art is operated, the combustion products such as carbon 6 in the intake chamber 22 are carried by a backflow 8 going toward the idle intake regulating valve 5 through the idle intake passageway 4 and are adhered to and deposited on the intake regulating valve 5 as indicated by 13 in FIG. 3. As a result, the flow path for the flow of air indicated as a forward flow 9 is narrowed. There is a possibility of error in the control of the flow rate as a result. In this case, if a maze-like narrow passageway part is provided at the downstream side of the intake regulating valve, not only will the flow of the idle intake be prevented, but also the combustion products will clog at the maze part and the passageway will easily become blocked.
Further, as a third related art, as in the idle intake control device 11 in the gasoline engine 1 shown in FIG. 4, a state of low load operation is shown, in which the throttle valve 3 is slightly open. Most of the intake air will pass through the upper and lower clearances 2a and 2b formed between the upper and lower circumferential edges 3a and 3b far away from the shaft 14 of the disk-like throttle valve 3 and the inner wall surface of the intake passageway 2. Additionally, the air flow will follow the flow lines 15 indicated by the arrows, and flow into the intake chamber 22. The upstream part of the idle intake passageway 4 from the idle intake regulating valve 5 is indicated as 4a. Additionally, the part of the idle intake passageway 4 up to an opening 16 at the terminal end at the downstream side from the idle intake regulating valve 5 is indicated as 4b. Since the opening 16 is provided in the wall surface of the intake passageway 2 at a position near the clearance 2b formed when the throttle valve 3 is slightly opened as in FIG. 4, one part of the intake air passing through the clearance 2b will not flow to the downstream side of the intake passageway 2. This part of the intake air will flow into the part 4b of the idle intake passageway 4 on the downstream side from the opening 16 as indicated by the flow line 17 marked by the arrow, and will further pass through the opening idle intake regulating valve 5, and flow back toward the upstream side part 4a.
In the intake chamber 22 of the engine 1, combustion products such as the carbon particles, are generated in the combustion chamber due to the blowback of combustion gas from combustion chamber to the intake chamber 22. This causes in a specific operational state and exhaust gas recirculation (EGR) is carried out for purification of the exhaust, always exist in a floating state or a state of unstable adhesion to the inner surface of the wall. Therefore, if part of the backflow 17 of intake air is produced in the idle intake passageway 4 as mentioned above, the combustion products existing in the intake chamber 22 will ride the backflow 17 and reach the idle intake regulating valve 5 where they will adhere. Thus, they are apt to reduce the controllability of the idle intake regulating valve 5.
Further, to explain a more general problem of the related art, a fourth related art of the intake system of the engine is shown in FIG. 5 and FIG. 6. In the same way as the above related art, external air 10 is sucked into the engine 1 through an intake pipe 21 and intake chamber 22 so as to maintain the rotation of the engine. An intake regulating valve 3 is disposed in the intake pipe 21 to regulate the amount of intake air. Further, in order to hold the amount of intake air at the time of idling when this intake regulating valve 5 is fully closed, for example, the idle intake control device 11 disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2-233817 is disposed.
The idle intake control device 11 is provided with, as shown in FIG. 6, an idle intake passageway 4 for connecting the upstream side and downstream side of the intake regulating valve 3 like the throttle valve and with an idle intake regulating valve 5 disposed in the middle of the same. In this case as well, when the intake regulating valve 3 is fully closed, intake air adjusted in amount by the idle intake regulating valve 5 is introduced into the intake chamber 22 through the idle intake passageway 4, is sucked into the engine 1 at the time of opening of the intake valve 12, and maintains the idling state.
In such an idle intake control device, generally there is a problem in that the combustion products of the engine 1 invade the idle intake passageway 4 due to the pulsation of the intake pressure in the intake chamber 22 when the intake regulating valve 3 is opened wide. Namely, when the intake regulating valve 3 becomes substantially fully open as shown in FIG. 6, the forward direction flow going from the upstream side to the downstream side in the idle intake passageway 4 dwindles to substantially zero. For this reason, in the idle intake passageway 4, a reciprocal direction flow as indicated by the arrows is generated due to the pulsation-like flow of intake air in the intake pipe 21. Due to this flow, the combustion products in the intake chamber 22 are liable to invade the internal portion of the idle intake passageway 4 from the outlet side thereof due to the blowback from the engine 1, flow back, and adhere to the idle intake regulating valve 5.